Anatomy and Surgical Approaches of the Forearm, Wrist, and Hand

Melissa A. Klausmeyer

Asif M. Ilyas

Chaitanya S. Mudgal

DEFINITION

Safe surgical dissection and exposure require an in-depth knowledge of anatomy. In no place is this more relevant than in the surgical approaches to the hand, wrist, and forearm.
The critical aspect of successful surgical approaches in the forearm and wrist is the use of internervous planes.
- These planes lie between muscles that are innervated by different nerves.
- Dissection through internervous planes allows extensive mobilization and exposure without risk of muscle denervation.
Unique to the hand, wrist, and forearm is the complex relationship of not only the muscles overlying bone but also the close proximity and delicate balance of accessory anatomic structures, including tendons, vessels, and nerves. Consideration of postoperative function of the extremity should start with preoperative surgical planning.
- Elective incisions should not cross flexion creases (antecubital fossa, wrist, or digit creases) to avoid scar contracture.
- If necessary, a transverse limb or zigzag incision should be incorporated to avoid crossing flexion creases perpendicularly.

ANATOMY

The anatomy of the hand, wrist, and forearm is intricate and can be discussed in many ways and in extensive detail. For the discussion in this chapter, anatomy will focus on the compartments of the hand and forearm and their relevance to surgical approaches (Table 1).

SURGICAL MANAGEMENT

All surgical approaches to the hand, wrist, and forearm warrant sound understanding of surface and deep anatomy, internervous planes, and surgical technique.
Planning the surgical approach begins by identifying reliable surface anatomy.

Preoperative Planning

Arrangements for instruments, sutures, microscope, imaging support, implants, and assistants should be made before the day of surgery.
Anatomy, radiographic templating, surgical approach, procedure, and alternatives should be reviewed.

Positioning

Most approaches to the hand, wrist, and forearm can be performed with the patient supine and the operative extremity extended on a hand table and the surgeon and assistants seated.
The hand table should be stable and well secured. It should allow adequate space for both the operative limb and the surgeon’s elbow and forearm to minimize fatigue and enhance stability and is usually placed so that the patient’s shoulder is level with the cephalad third of the table, allowing the hand to be placed on the table without undue abduction of the shoulder.
The stool should be stable and comfortable, with the height set such that the knees are level with the hips and the feet are resting flat on the ground.
The lights should be angled directly over the hand table and not from behind the surgeon or assistant’s shoulder to prevent shadows on the operative field.
Loupe or microscope magnification is often essential for good visualization in upper extremity surgery.
The use of a pneumatic tourniquet (either sterile or unsterile) is advised to maintain a bloodless field and clear visualization of all anatomic structures.

Approach

Multiple approaches to the hand, wrist, and forearm exist and are best divided into the anatomic site and direction of exposure.
The approach should be chosen based on the indication for surgery.

Table 1 Compartments of the Hand and Forearm

Compartments	Origin	Insertion	Innervation
Thenar
Abductor pollicis brevis	Trapezium/scaphoid	Radial base of thumb P1	Median (recurrent motor branch)
Flexor pollicis brevis	Trapezium	Base of thumb P1	Median (recurrent motor branch)
Opponens pollicis	Trapezium	Radial base of thumb P1	Median (recurrent motor branch)
Adductor
Adductor pollicis	Capitate/third metacarpal	Ulnar base of thumb P1	Ulnar
Hypothenar
Abductor digiti minimi	Pisiform	Ulnar base of small P1	Ulnar
Flexor digiti minimi brevis	Hook of hamate	Base of small P1	Ulnar
Opponens digiti minimi	Hook of hamate	Ulnar base of small P1	Ulnar
Interosseous
Dorsal interossei (4)	#2, 3, 4, 5 metacarpals	Radial or ulnar base of P1	Ulnar
Volar interossei (3)	#2, 4, 5 metacarpals	Radial or ulnar base of P1	Ulnar
Carpal Tunnel
Flexor digitorum profundus and superficialis tendons, lumbricals, flexor pollicus longus tendon, median nerve	Hook of hamate	Scaphoid tubercle
Superficial Volar Forearm
Pronator teres	Medial epicondyle	Mid-third of radius	Median
Flexor carpi radialis	Medial epicondyle	Base of #2 MC	Median
Palmaris longus	Medial epicondyle	Palmar fascia of hand	Median
Flexor carpi ulnaris	Medial epicondyle	Pisiform/base of #5 MC	Median
Flexor digitorum superficialis	Medial epicondyle	Base of #2, 3, 4, 5 P2	Median
Deep Volar Forearm
Flexor digitorum profundus	Ulna/interosseous membrane	Base of #2, 3, 4, 5 P3	#2, 3 – Median (ant. interosseous branch) #4, 5 – Ulnar nerve
Flexor pollicis longus	Distal third of radius	Base of thumb P2	Median (ant. interosseous branch)
Pronator quadratus	Distal third of ulna	Distal third of radius	Median (ant. interosseous branch)
Dorsal Forearm
Abductor pollicis longus	Mid-third dorsal radius	Radial base of thumb MC	Radial (post. interosseous branch)
Extensor pollicis brevis	Mid-third dorsal radius	Dorsal base of thumb P1	Radial (post. interosseous branch)
Extensor pollicis longus	Dorsal ulna	Dorsal base of thumb P2	Radial (post. interosseous branch)
Extensor digitorum communis	Lateral epicondyle	Dorsal base of #2, 3, 4, 5 P3	Radial (post. interosseous branch)
Extensor indicis proprius	Dorsal ulna	Dorsal base of #2 P3	Radial (post. interosseous branch)
Extensor digiti quinti	Lateral epicondyle	Dorsal base of #5 P3	Radial (post. interosseous branch)
Extensor carpi ulnaris	Lateral epicondyle	Dorsal base of #5 MC	Radial (post. interosseous branch)
Supinator	Lateral epicondyle	Proximal third of radius	Radial (post. interosseous branch)
Mobile Wad
Brachioradialis	Lat. condyle humerus	Distal radius styloid	Radial
Extensor carpi radialis longus	Lat. condyle humerus	Dorsal base of #2 MC	Radial
Extensor carpi radialis brevis	Lat. condyle humerus	Dorsal base of #3 MC	Radial (post. interosseous branch)
P1, proximal phalanx; P2, middle phalanx; P3, distal phalanx; ant., anterior; MC, metacarpal; post., posterior; lat., lateral.

TECHNIQUES

▪ Skin Incisions of the Hand

Incisions should be outlined by sterile surgical markers before making the actual incision to confirm appropriate position, to confirm the adequacy of skin bridges should multiple incisions be used, and to help guide closure.
Incisions can be made in skin creases on the volar aspect of the hand, but incisions in deep creases should be avoided due to the thin subcutaneous tissue, tendency for maceration due to moisture, and tendency toward poor apposition of skin edges on closure.
Incisions perpendicular to a volar flexion crease should be avoided to prevent scar formation and secondary skin contractures that can lead to loss of motion and functional impairment (TECH FIG 1A,B).

TECH FIG 1 • Examples of volar (A,B) and dorsal (C) incisions for the hand and digits.
Incisions on the dorsal surface of the hand can be smaller due to the more mobile and loose nature of the dorsal skin (TECH FIG 1C).
- Vertical, horizontal, and curved incisions can all be used with good facility as long as adequate skin bridges are maintained.
Fingers can be exposed dorsally, volarly, or midaxially.
- Dorsal incisions can be longitudinal or curvilinear.
- Volar incisions are best facilitated by a zigzag pattern (Bruner incision) that cross creases laterally and at angles.
- Midaxial incisions are best placed at the junction of glabrous and nonglabrous skin, with attention being paid to the neurovascular bundle that sits in the plane of the flexor sheath. The neurovascular bundle can be taken volarly with the volar flap or can be left in place by carrying the dissection superficial to it.

▪ Approach to the Nail Bed

The nail plate is removed bluntly from the underlying sterile matrix and overlying eponychium.
Longitudinal incisions are made at the radial and ulnar edges of the eponychium to expose the proximal nail bed and germinal matrix.

▪ Approach to the Interphalangeal Joints